Personal computers are typically non-real-time operation machines. In order to provide them with real-time operation, such as is necessary to provide facsimile, modem, audio or other operation, separate components, often provided as add-on cards, are added to the personal computer. The components include processing units, separate from that of the personal computer itself, which respond in real-time to the incoming and outgoing signals. Thus, there are modem cards, fax cards, fax/modem cards, telephony cards, audio cards, etc. Each card includes its own digital signal processing (DSP) unit which ensures that the response time is as expected. This is of particular importance for fax and modem cards.
FIG. 1, to which reference is now made, illustrates a prior art audio component, such as the AWE32 PnP card by Creative Technology Ltd. of Singapore which implements the SoundBlaster standard. It comprises an audio interface unit 10, a DSP unit 12, a buffer unit 14 and a bus interface 16. The audio interface 10 connects to one or several input devices, such as a PC, CD ROM, a line in for receiving other audio signals, and a microphone. The output of the audio interface 10 is typically to stereo speakers. The audio interface 10 processes the input signals to the point of their conversion to digital signals and prepares the analog output signals from the digital ones.
The DSP unit 12 typically further processes the signals, such as compressing and decompressing them (so that they occupy less space in the computer) and/or generating selected sounds (known as "FM synthesis"). For FM synthesis, the DSP unit 12 receives "audio commands" indicating which FM signals should be synthesized. The FM synthesizing operation can also be performed by a separate unit.
The buffer unit 14 buffers the signals between the computer, which runs at one speed, and the audio interface unit 10, which typically runs at a different speed, i.e. the speed of the input devices. The buffer unit 14 also provides the digital signals to the PC bus interface 16 by which the signals enter the personal computer.
The audio interface unit 10 includes an input section 18 and an output section 20, each of which has left and right channels, thereby to provide stereo audio signals. Per channel, the input section 18 employs an analog to digital (A/D) converter 22 having a variable sampling rate of between 8 and 44 KHz, an anti-aliasing filter 24 and, a mixer to select the source of the input and output signals, if the audio component is connectable to several input and output devices. The anti-aliasing filter 24 typically is an analog low pass filter which filters out all signals and noise above half the sampling rate. The output section 20 also has a mixer 26 and anti-aliasing filter 24 per channel. In addition, the output section has a digital to analog (D/A) converter 28 per channel, for converting the output signals of the DSP unit 12 to analog signals which are later filtered by the anti-aliasing filter 24. The A/D and D/A converters typically have an accuracy of 75-85 dB.
The prior art audio component typically also has several input and output channels (labeled 30) for logic signals and interrupt registers and/or counters 32 which typically are connected between the logic ports 30 and the bus interface 16.
Operating with the audio component, on the personal computer side, is an audio application. If the sound application is a "DOS sound application" 21 operating with the MS-DOS.TM. operating system, of Microsoft of the USA, then the sound application communicates directly with the audio component. If the sound application is a "WINDOWS sound application" 25, operating with the WINDOWS.TM. operating system, also of Microsoft, the sound application communicates with the audio component via an audio driver 23.
FIG. 2A, to which reference is now made, illustrates a typical prior art modem card. It comprises a data access arranging (DAA) unit 39, two channels, for input and output, respectively labeled 40 and 42, a modem DSP unit 44, a modem buffer unit 46 and a modem bus interface 48. The DAA 39 provides the physical line interface for the modem signals and handles the telephony operations of dialing, on/off hook detection and ring detection in accordance with instructions from the DSP unit 44. The input and output channels 40 and 42 each have an anti-aliasing filter 50 and respectively have an A/D converter 52 and a D/A converter 54. The converters 52 and 54 typically sample the signals at 8 or 9.6 KHz and the anti-aliasing filters 50 typically have a cutoff frequency of 4 KHz.
The modem DSP unit 44 processes the incoming and outgoing signals in accordance with standard modem practice. This includes converting the signals between symbol format and bit format, modulating and demodulating the symbol format signal onto a carrier frequency, etc. In addition, the modem DSP unit 44 handles the initiation of dialing, on/off hook detection, ring detection and the inter-modem communication ("handshaking") indicating that each symbol is received correctly.
As in the audio component, the modem buffer unit 46 buffers the signals between the computer and the channels 40 and 42. The modem buffer unit 46 also provides the digital signals to the bus interface 46 by which the signals enter the personal computer. A modem application 49 on the personal computer, such as PCPLUS.TM. or BITCOM.TM., then further processes the signals.
Native or host signal processing is a technique which utilizes the host CPU, rather than the DSP chip on the card, for processing of the real-time signals of a peripheral card. This requires that the host CPU be able to respond in a real-time manner to the signals being sent by the modem on the other side of the conversation.
PCTEL Inc. of San Jose, Calif., USA has announced a native signal processing modem whose full set of components are illustrated in FIG. 2A, to which reference is now briefly made. FIG. 2A illustrates the modem application 49, the NSP (software) modem 47 on the personal computer side and a digital interface 45, a codec 43 and the DAA 39 on the peripheral side. The codec 43 converts the data between analog and digital formats and the digital interface 45 provides buffering and interface operations between the codec 43 and the personal computer.
Crystal Semiconductor Corporation of Austin, Tex., USA has illustrated, an audio/telephony multifunction multimedia adapter, the CRD4232-2 which combines a number of Crystal and Cirrus Logic chips. The adapter is a single PC peripheral card which processes both audio and telephone signals. The adapter has separate subsystems for the telephone and audio operations; just a controller and a codec (coder/decoder) are shared.
Other companies, such as BestData, Boka and Creative have marketed combined audio/telephony cards and U.S. Pat. No. 5,526,408 to Yekutiely describes a telephony addition to an audio card.